Field of the Invention
CRTs (cathode ray tubes) have been widely used as display apparatus in the TV field and as output-input display apparatus for computers. Recently, plasma displays have been developed for use in place of CRTs. The plasma displays can be classified depending upon the driving method used, i.e., a DC type display driven by applying DC voltage and an AC type display driven by applying AC voltage. The DC type display has been widely used for miniature computers and meters which display figures and characters.
The present invention relates to an AC type plasma display which was disclosed in the Fall Joint Computer Conference in the U.S.A. on Nov. 1966 by H. D. Slottow and D. L. Bitzer of Illinois University.
The plasma display has the following unique characteristics: A memory function is incorporated in the plasma display itself. The purpose of the memory function is to provide a switching operation for switching the ON state and OFF state of picture elements by applying a turn-on or turn-off pulse while applying a sustaining drive voltage to the plasma panel. The plasma display is more suitable as the output-input display for a computer because of the characteristic of the memory function.
A CRT has no memory function so that a stationary image cannot be maintained without continuous refresh scanning. Moreover, the plasma display is a matrix array display in which picture elements are arranged in lattice form. Accordingly, the picture elements of luminescent points are usually stationary which yields an excellent image display having high accuracy. Furthermore, the panel is transparent and comprises a thin flat plate and has a simple structure, so that a large size panel can be easily prepared. Power consumption of the panel is relatively small and no crosstalk is present.
However, the plasma display has the following disadvantages: The states of the picture elements are only the two states of ON and OFF so that a half-tone is difficult to display. The discharge occurs in certain areas so that it is difficult to attain a high resolving power of less than 0.3 mm of the picture element pitch. The electrodes are arranged to form a matrix and each of the electrodes should be switched which complicates the switching circuit. The half-tone problem has been studied and overcome to provide an image having plural tones by a method of controlling the number of luminescent operations utilizing the difference of a wall voltage and a method of a time modulation within each frame display time. The resolving power problem is not serious because the resolving power of a TV set is usually 0.5 - 1.0 mm.